Integrated circuit comprising a single photon avalanche diode and corresponding manufacturing method

ABSTRACT

A single photon avalanche diode (SPAD) includes a PN junction in a semiconductor well doped with a first type of dopant. The PN junction is formed between a first region doped with the first type of dopant and a second region doped with a second type of dopant opposite to the first type of dopant. The first doped region is shaped so as to incorporate local variations in concentration of dopants that are configured, in response to a voltage between the second doped region and the semiconductor well that is greater than or equal to a level of a breakdown voltage of the PN junction, to generate a monotonic variation in the electrostatic potential between the first doped region and the semiconductor well.

PRIORITY CLAIM

This application claims the priority benefit of French Application forPatent No. 2012999, filed on Dec. 10, 2020, the content of which ishereby incorporated by reference in its entirety to the maximum extentallowable by law.

TECHNICAL FIELD

Embodiments and implementations relate to integrated circuits, inparticular integrated circuits including at least one single photonavalanche diode (SPAD).

BACKGROUND

A SPAD is a semiconductor device based on a bipolar junction (PNjunction) that is reverse polarized at a voltage exceeding the breakdownvoltage of the junction.

The electric field resulting from the polarization is very high (forexample greater than 5*10⁵ V/cm) such that a single charge carrierinjected into the space charge area, for example generated byphotoelectric effect, can trigger a self-sustained avalanche of chargecarriers. A quenching circuit allows for stopping the avalanche effectand reset the SPAD diode to the polarization exceeding the breakdownvoltage.

FIG. 1A illustrates an example of the structure of a depleted SPADdiode. To increase the size of the charge collection area, an intrinsicor quasi-intrinsic region I between the anode region P+ and the cathoderegion N+ is provided. To compensate for the increase in breakdownvoltage resulting from the presence of this intrinsic region I, a regionP is interposed between the cathode region N+ and the intrinsic regionI.

However, this type of structure introduces a parasitic effect of“pockets” of charge carriers during the quenching of an avalanche, wherethe charges generated are trapped by an electrostatic potential barrierlocated substantially between the depleted anode region P and theintrinsic region I. This parasitic effect of pockets of carriers has theconsequence of introducing parasitic secondary avalanches (usually“lags”) disturbing the detection mechanism. Secondary parasiticavalanches caused when resetting the SPAD diode by the presence ofcharge pockets trapped in the active avalanche region have a detrimentaleffect on the performance of the device.

Reference is made in this regard to FIGS. 1B and 1C, where FIG. 1Billustrates lines of electrostatic equipotentials in a section of thevolume of an embodiment of a SPAD diode having the structure of FIG. 1A,when the potential difference between the anode P+ and the cathode N+ isat the breakdown voltage; and where FIG. 1C illustrates the shape of theelectrostatic potential PE along the axis Z of FIG. 1B.

The solid line curve in FIG. 1C represents the electrostatic potentialwhen the SPAD diode is quenched, for a value close to the breakdownvoltage Vb of the PN junction. The dotted curve in FIG. 1C representsthe electrostatic potential when the SPAD diode is reset, at a voltageVb+Vex greater than the breakdown voltage Vb of the PN junction by anamount Vex. It can be seen on these curves that a potential well PKT isformed at the breakdown voltage Vb, when the SPAD diode is quenched.Thus, charges can remain trapped in the potential well PKT, whichautomatically triggers a parasitic avalanche effect when resetting toVb+Vex.

Conventional solutions reducing the concentration of dopants in thedepleted anode region P allow to limit the depth of the potential wells,but also introduce a loss in sensitivity of the diode called the photondetection probability (PDP).

There is therefore a need to guard against parasitic detection phenomena(“lags”) without reducing the photon detection probability.

SUMMARY

According to one aspect, an integrated circuit comprises at least onesingle photon avalanche diode “SPAD” including a PN junction, in asemiconductor well doped with a first type of dopant, between a firstregion doped with the first type of dopant, called the avalanche region,and a second region doped with a second type of dopant opposite to thefirst type of dopant. According to a general feature of this aspect, thefirst doped region is shaped so as to incorporate local variations inthe concentration of the dopants, adapted to generate a monotonicvariation in the electrostatic potential between the first doped regionand the semiconductor well, when the voltage between the second dopedregion and the semiconductor well is greater than or equal to the levelof the breakdown voltage of the PN junction.

For example, the first type of dopant is the P type, that is to say theacceptor type, and the second type of dopant is the N type, that is tosay the donor type. The semiconductor well may constitute thequasi-intrinsic (that is to say, lightly doped) region, the first dopedregion may constitute the depleted anode region, and the second dopedregion may constitute the cathode region of the SPAD diode.

The variations in the concentration of the dopants of the first dopedregion defined according to this aspect correspond, for example, to moreweakly locally doped areas, so as not to generate a potential well (thatis to say, reciprocally, so as to generate a monotonic variation in theelectrostatic potential) at the corresponding positions. The chargecarriers are not retained in pockets and can thus flow completely in theelectric current of the polarized diode at the breakdown voltage (inparticular during a quenching phase).

It will be noted that a potential well for a charge of a given polarity(for example positive) is a potential barrier for a charge of oppositepolarity (respectively negative), and necessarily has a non-monoticityin the electrostatic potential, that is to say that the variation of theelectrostatic potential is increasing in one interval and decreasing inanother interval.

Furthermore, the variations in the concentration of dopants being localand not global, the remainder of the first doped region, that is to saythe remainder of the avalanche region, can consequently be configured tomaintain a significant electric field and thus remain efficient in termsof photon detection probability.

The variations in the concentration of dopants and their effects can beobserved for example by means of Transmission Electron Microscopy (TEM),or by means of EMission MIcroscopy (EMMI) allowing to visualize theavalanche areas which emit photons.

According to one embodiment, the second doped region is located on thesurface of the semiconductor well at a position centered in aphotosensitive area of the SPAD diode, the first doped region comprisesa first volume at the position centered at a depth in contact with thebottom of the second doped region, and a second annular volume laterallysurrounding the first volume and at a depth remote from the second dopedregion but joining the depth of the first volume.

The first volume of the first doped region thus allows to construct theactive region wherein the avalanche effects occur, while the secondvolume of the first doped region, located on the periphery of the activeregion, allows to electrically connect the first volume with contactpoints usually located on the surface of the well.

Furthermore, the first annular volume usually acts as a point forfocusing carriers towards the avalanche region, preventing carriers frombeing evacuated through another route. Consequently, when recharging thediode, the carriers conventionally cannot pass through the annularvolume.

However, according to one embodiment, the first volume and the secondvolume are laterally spaced apart by a gap, and said local variations inthe concentration of dopants comprise areas for diffusing dopants insaid gap having a lower concentration of dopants than in the firstvolume and the second volume.

Thus, the local variations in the concentration of the dopant in the gapprovide an evacuation route for carriers during diode recharging(“quenching”). Furthermore, to prevent lateral breakdown of the firstdoped region, the electric field is intentionally reduced by moving theannular region (second volume) away from the main breakdown region(first volume).

Advantageously, the second volume further comprises a pattern locallypassing through said gap to join the first volume (that is to say theavalanche region) in at least one position, so as to ensure electricalconduction between the second volume and the first volume.

Thus, the electrical conduction between the first and second volumes ofthe first doped region is not degraded in return for the presence ofsaid gap providing an evacuation route for carriers trapped duringrecharging (“quenching”).

According to one embodiment, the first volume and the second volume arelaterally joined together and said local variations in the concentrationof the dopants comprise areas in the first volume having a lowerconcentration of dopants than in the second volume.

Advantageously, the second volume further comprises a pattern inside thefirst volume, locally increasing the dopant concentration in the firstdoped region.

According to another aspect, a method is provided for manufacturing anintegrated circuit comprising at least one single photon avalanche diode(SPAD). The method comprises, in a semiconductor well doped with a firsttype of dopant, an implantation of a first region doped with the firsttype of dopant, called an avalanche region, and an implantation of asecond region doped with a second type of dopant opposite to the firsttype of dopant, so as to form the PN junction of the SPAD diode.According to a general feature of this aspect, the implantation of thefirst doped region comprises forming local variations in theconcentration of the dopants, adapted to generate a monotonic variationin the electrostatic potential between the first doped region and thesemiconductor well, when the voltage between the second doped region andthe semiconductor well is greater than or equal to the level of thebreakdown voltage of the PN junction.

According to one implementation, the second doped region is implanted onthe surface of the well at a position centered in a photosensitive areaof the SPAD diode, the implantation of the first doped region comprisesa first implantation of a first volume at the centered position at adepth in contact with the bottom of the second doped region, and asecond implantation of a second annular volume laterally surrounding thefirst volume and at a depth remote from the second doped region butjoining the depth of the first volume.

According to one implementation, the first volume and the second volumeare implanted so as to be laterally spaced apart by a gap, and saidlocal variations in the concentration of dopants comprise areas fordiffusing dopant in said gap having a lower concentration of dopantsthan in the first volume and the second volume.

Advantageously, the second implantation of the second volume furthercomprises an implantation of a pattern locally passing through said gapto join the first volume in at least one position, so as to ensureelectrical conduction between the second volume and the first volume.

According to one implementation, the first volume and the second volumeare implanted so as to be laterally joined together, the firstimplantation of the first volume being made at a concentration ofdopants less than the concentration of dopants of the second volume, andsaid local variations in the concentration of dopants comprise areas inthe first volume having a lower concentration of dopants than in thesecond volume.

Advantageously, the second implantation of the second volume furthercomprises an implantation of a pattern inside the first volume, locallyincreasing the dopant concentration in the first doped region.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features of the invention will become apparent uponexamining the detailed description of embodiments and implementations,which are in no way limiting, and of the appended drawings, wherein:

FIG. 1A illustrates an example of the structure of a depleted singlephoton avalanche diode (SPAD);

FIG. 1B illustrates lines of electrostatic equipotentials in a sectionof the volume of the SPAD having the structure of FIG. 1A;

FIG. 1C illustrates the shape of the electrostatic potential PE alongthe axis Z of FIG. 1B;

FIG. 2A illustrates a top view of a SPAD;

FIGS. 2B and 2C illustrate sectional views of the SPAD in FIG. 2A;

FIG. 2D illustrates the shape of the electrostatic potential;

FIGS. 3A and 3B illustrate a top view and a sectional view,respectively, of another embodiment of a SPAD;

FIGS. 4A and 4B illustrate a top view and a sectional view,respectively, of a variant of a SPAD; and

FIGS. 5A and 5B illustrate a top view and a sectional view,respectively, of a variant of a SPAD.

DETAILED DESCRIPTION

FIG. 2A illustrates a top view of a single photon avalanche diode (SPAD)SPD of an integrated circuit IC. For reasons of readability regardingthe reference SPD, the acronym “SPAD”, usually in uppercase letters,will be written in lowercase letters “spad” in the following.

FIG. 2B illustrates a sectional view of the spad diode SPD in the planeBB of FIG. 2A, and shows the various semiconductor regions of the spaddiode SPD.

FIG. 2C illustrates a sectional view of a volume of the spad diode SPDin the volume CC of FIG. 2A, and shows the lines of electrostaticequipotentials during a polarisation of the spad diode SPD at a voltageclose to the breakdown voltage of its PN junction.

FIG. 2D illustrates the shape of the electrostatic potential Pot alongthe axis Z of FIGS. 2B and 2C.

Reference is made to FIGS. 2A and 2B.

The diode SPD includes a PN junction between a first region PAN dopedwith a first type of dopant, and a second region N+ doped with a secondtype of dopant opposite to the first type.

Arbitrarily, the first type of dopant is chosen as the P type, that isto say acceptor dopants, and the second type of dopant is chosen as theN type, that is to say donor dopants. Equivalent structures having theopposite doping types can be considered.

A cathode region of the diode SPD includes the second doped region N+,which is strongly doped of the N type, implanted on the surface at afront face FA of the semiconductor device of the integrated circuit CI.

The cathode region N+ is located, in the plane of FIG. 2A, at a positioncentered in a photosensitive area of the diode SPD. The photosensitivearea of the diode corresponds to the interface between the first dopedregion N+ and the second doped region PAN.

Local areas of the surface of the second doped region N+ can be adaptedto provide a good ohmic contact connection, typically contact pointsincluding a thin layer of metal silicide (not shown).

An anode region of the diode SPD comprises different P-type dopedsemiconductor regions, including in particular the first doped regionPAN, a lightly doped semiconductor well P−, sometimes referred to as“quasi-intrinsic” region, and an anode terminal region P+ at the bottomof the well P−. The semiconductor well P− is, for example, formed by anin-situ doped epitaxy step, or by low concentration doping of anintrinsic substrate or of an intrinsic epitaxial layer.

The upper surface of the semiconductor well P− defines the front face FAof the semiconductor part of the integrated circuit CI.

The anode terminal region P+, at the bottom of the semiconductor wellP−, may be formed by implantation of dopants before or after theformation of the semiconductor well P−.

The first doped region PAN includes a first volume, called the depletedanode region P or else the avalanche region, implanted at a depthadapted for the top of the depleted anode region P to be in contact withthe bottom of the second doped region N+.

The depleted anode region P is located, in the plane of FIG. 2A, at aposition centered opposite the cathode region N+.

The actual PN junction of the diode SPD is thus located at the interfacebetween the depleted anode region P and the second doped cathode regionN+.

The term “depleted anode region” comes from the fact that the spacecharge area ZCE (FIGS. 2C and 2D) completely encompasses the depletedanode region P when the spad diode SPD is “reset”, that is to say,reverse polarized at a voltage greater, for example by +4V, than itsbreakdown voltage.

The anode region further includes a second volume, referred to herein asthe anode ring Prg, implanted in an annular shape laterally surrounding(that is to say in the plane of FIG. 2A) the first volume P, and at adepth remote from the second doped region N+ but joining the depth ofthe first volume P (FIG. 2B).

The anode region further includes contact wells PW formed on the sidecontour of the anode ring Prg to electrically connect the anode P+terminal and the anode ring Prg to ohmic contact points located at thefront face FA. The ohmic contact points can conventionally comprise aheavily doped region cntP+ and a metal silicide layer (not shown).

During the manufacture of the spad diode SPD, the first volume P and thesecond volume Prg are implanted in areas which are spatially defined byimplantation masks, typically made of photolithographed resin. Theimplantation masks spatially define the implantation areas, in the planeof FIG. 2A, so that the first volume P and the second volume Prg arelaterally spaced by the gap DST.

After the implantations of the first volume P and of the second volumePrg, a phenomenon of diffusion of the implanted doping particles forms adecreasing dopant concentration gradient on the contour of the volumesP, Prg, called dopant diffusion areas Pdiff.

The dopant diffusion areas Pdiff occupy said gap DST between the firstvolume P and the second volume Prg, with a lower concentration ofdopants than in the depleted anode region P (first volume) and the anodering Prg (second volume).

Consequently, the first doped region PAN comprises local variations indopant concentration, at the dopant diffusion areas Pdiff in the gapsDST separating the depleted anode region P and the anode ring Prg.

Note that the axis Z of FIG. 2B is positioned to pass through one ofsaid local inhomogeneities of the dopant concentration in the firstdoped region PAN.

Furthermore, to ensure electrical conduction between the depleted anoderegion P and the anode ring Prg despite the gap DST separating them, thestep of implanting the second volume comprises implanting a patternPcrx, locally passing through said gap DST in order to join the firstvolume P in at least one position.

The pattern Pcrx, implanted during the implantation of the secondvolume, consequently has the same dopant concentration and depth as theanode ring Prg.

The pattern may comprise bands of dopants diametrically passing throughthe inside of the ring shape of the second volume Prg, having a verticalposition partially incorporated into the first volume P.

In this example, the pattern Pcrx has the shape of a cross with twoperpendicular branches.

Alternatively, portions of bands directed radially towards the inside ofthe ring shape of the second volume Prg can join the first volume Pwithout diametrically passing therethrough, reference may be made to therepresentation of FIG. 5A in this regard, in particular the elements PH1of the pattern of FIG. 5A.

Reference is now made to FIGS. 2C and 2D.

It will be recalled that FIG. 2C shows the electrostatic equipotentialsin a perspective view of the volume CC of the diode SPD of FIG. 2A, andFIG. 2D illustrates the shape of the electrostatic potential Pot alongthe axis Z of FIGS. 2B and 2C.

The various doped semiconductor regions P+, P−, Prg, Pcrx, P, N+ are notspecifically shown in FIG. 2C but are nevertheless identified in thevolume by their respective references.

The levels of the electrostatic potential are represented in FIGS. 2Cand 2D in the case where the diode SPD is reverse polarized, between thecathode region N+ (second doped region) and the semiconductor well P−,at a voltage close to the breakdown voltage of the PN junction.

For example, the voltage close to the breakdown voltage is comprisedbetween the breakdown voltage Vb and 1 (one) volt above the breakdownvoltage Vb+1 volts.

In absolute terms, the reverse polarization is transmitted from thepoints of contact on the front face FA, and the voltage is strictlyspeaking defined between the cathode region N+ and the anode terminalregion P+. However, it is considered that the voltage of thesemiconductor well P− is equal to the voltage of the anode terminalregion P+ (excluding avalanche phenomenon).

Unlike the conventional case illustrated by FIGS. 1B and 1C, the shapeof the electrostatic potential Pot along the axis Z (drawn in FIGS. 2Band 2C) does not have a potential well or barrier capable of trappingthe charges generated during an avalanche effect, and consequently thespad diode SPD does not undergo the problems associated with chargecarrier pockets.

Indeed, the local variations in the concentration of the dopants in thefirst doped region PAN generate a monotonic variation in theelectrostatic potential Pot in their proximities between the first dopedregion PAN and the semiconductor well P− (that is to say anever-increasing variation of the electrostatic potential Pot, from thesemiconductor well P− to the first doped region PAN), when the voltagebetween the cathode region N+ and the semiconductor well P− is at thebreakdown voltage of the PN junction.

Thus, all charges generated during an avalanche effect can circulatebetween the cathode region N+ and the anode terminal region P+ and aredischarged into the avalanche current of the spad diode SPD.

As a result, the avalanche current quenching mechanisms reinitialize andreset the spad diode SPD to a completely depleted state and theparasitic avalanche triggering (“lag”) caused by the pockets of chargecarriers trapped by a potential barrier does not occur.

It will be noted that the electrostatic potentials of FIGS. 1B and 2C inparticular are the results of finite element simulations of theTechnology Computer-Aided Design (TCAD) type, having in particular thesame mathematical model and the same calculation parameters.

The difference between the two simulations lies in the structure of thedepleted anode region P and of the anode ring Prg implanted so as tocomprise local variations in the concentration of the dopants, aspreviously described in relation to the FIGS. 2A and 2B; while for theresults of FIG. 1B, the equivalent doped regions are joined togetherwith a homogeneous concentration of dopants.

From the point of view of the performance of the spad diode SPD, inparticular the photon detection probability “PDP”, since the variationsin dopant concentration are locally defined by the alignments of theimplantations of the depleted anode region P and of the anode ring Prg(that is to say the implantations of the constituents of the first dopedregion PAN), the “overall” concentration of dopants in the second dopedregion PAN, in particular in the depleted anode region P, is notreduced, which does not reduce the performance of the SPAD diode.

The presence of the additional pattern Pcrx implanted with the anodering Prg is particularly advantageous for maintaining, and evenimproving, the performance, in particular the “PDP”, of the diode SPD.

Indeed, the concentration of dopants in the depleted anode region P, ormore widely in the second doped region PAN, can be increased in order toimprove the performance of the diode SPD, in particular the “PDP”,without undergoing the conventional counterpart of an increase inparasitic triggers “lags”.

FIGS. 3A and 3B illustrate another embodiment of a spad diode SPDwherein the first doped region PAN comprises local variations in theconcentration of dopants, adapted to generate a monotonic variation inthe electrostatic potential between the first doped region PAN and thesemiconductor well P−.

FIG. 3A shows a top view of the diode SPD, and FIG. 3B shows a sectionalview in the plane BB of FIG. 3A.

The elements common to the example described in relation to FIGS. 2A to2D bear the same references will not all be detailed again.

The first doped region PAN again comprises a first volume composed ofthe depleted anode region P, and a second volume composed of the anodering Prg and a pattern Pcrx joining the first volume P and implanted atthe same time as the anode ring Prg.

In this example, the depleted anode region P and the anode ring are notimplanted with a gap therebetween (see, reference DST—FIGS. 2A, 2B), butthe outer edge of the depleted anode region P and the inner edge of theanode ring are precisely aligned, with the tolerance of masking andimplantation techniques.

The concentration of the dopants of the depleted anode region P ischosen so as to generate a monotonic variation in the electrostaticpotential between the depleted anode region P and the semiconductor wellP−, at a polarization between the cathode region N+ and thesemiconductor well P− equal to the breakdown voltage of the PN junction.

In particular, the concentration of the dopants of the first volume P ischosen to be less than the concentration of the dopants of the secondvolume Prg, Pcrx.

In this example, the pattern Pcrx joins the first volume P, in order tolocally increase the dopant concentration in the first doped region PAN.

The pattern can comprise bands of dopants Pcrx diametrically passingthrough the inside of the ring shape of the second volume Prg, having avertical position partially incorporated in the first volume P, againillustrated in the example of a cross with two perpendicular branches.

In other words, the first doped region PAN comprises local variations inthe concentration of dopants, adapted to generate a monotonic variationin the electrostatic potential between the first doped region PAN andthe semiconductor well P−.

In this example, the variations in the concentration of dopants arelocated locally in the four quarters q1, q2, q3, q4 of the first volumeP, delimited by the two branches Pcrx of the pattern.

Thus, on the one hand, the local variations in the concentration ofdopants, in the first doped region PAN, comprise areas q1-q4 in thefirst volume P having a lower concentration of dopants than in thesecond volume Prg, which allow not to generate parasitic triggers“lags”. On the other hand, the highest dopant concentration of the firstdoped region PAN, in the second volume Prg, Pcrx, allows to ensure goodperformance, in particular “PDP”.

FIGS. 4A and 4B illustrate a variant of the exemplary embodiment of thespad diode SPD described in relation to FIGS. 3A and 3B, the commonelements bear the same references and will not all be detailed again.

FIG. 4A shows a top view of the diode SPD, and FIG. 4B shows a sectionalview in the plane BB of FIG. 4A.

In particular, in the first doped region PAN, the depleted anode regionP (first volume) has a dopant concentration less than the dopantconcentration in the anode ring Prg (second volume).

In this variant, the first volume P and the second volume Prg areimplanted so as to be joined together on a lateral overlapping portionRCV, in a common vertical portion (the depth of the two volumes isidentical to the previous descriptions in relation to FIGS. 2A to 3B).

The overlapping RCV of the first volume and the second volume ensuresthe electrical conduction of the anode ring Prg with the depleted anoderegion P.

Furthermore, in this variant, the second volume comprises a patternPcrc, having the shape of a disc implanted in the center of the diode(in the view of FIG. 4A), inside the first volume P. The pattern Pcrcthus locally increases the dopant concentration in the first volume P ofthe first doped region PAN.

In this variant, the local variations in the concentration of thedopants are formed by the lower concentration of the depleted anoderegion P in a bracelet-shaped area, the inner periphery of which isradially delimited by the perimeter of the disc Pcrc of the secondvolume, and the outer periphery of which is radially delimited by theinner perimeter of the anode ring Prg of the second volume.

Here again, on the one hand, the local variations in the concentrationof dopants, in the first doped region PAN, comprise the bracelet-shapedarea of the first volume P having a lower concentration of dopants thanin the second volume Prg Pcrc, and allow not to generate parasitictriggers “lags”. On the other hand, the higher concentration of dopantsin the first doped region PAN, in the second volume Prg, Pcrc, ensuresgood performance, in particular “PDP”.

FIGS. 5A and 5B illustrate another variant of the exemplary embodimentof the spad diode SPD described in relation to FIGS. 3A and 3B, thecommon elements bear the same references and will not all be detailedagain.

FIG. 5A shows a top view of the diode SPD, and FIG. 5B shows a sectionalview in the plane BB of FIG. 5A.

In particular, in the first doped region PAN, the depleted anode regionP (first volume) has a dopant concentration lower than the dopantconcentration in the anode ring Prg (second volume).

In this other variation, the second volume comprises, in addition to theanode ring Prg, a pattern PH1, PH2 penetrating inside the first volumeP, to locally increase the dopant concentration in the first dopedregion PAN.

The pattern includes band shapes PH1 radially directed inwardly of thering shape of the second volume Prg and penetrating in the first volumeP without diametrically passing therethrough.

The pattern includes square shapes PH2, two sides of which and onevertex penetrate in the direction of the diagonal of the square towardsthe center of the first volume P.

In the example of FIG. 5A, the shapes PH1, PH2 of the pattern of thesecond volume draw an identifiable contour with two perpendicular andsuperimposed “H” letters.

This example of a pattern allows to reinforce the dopant concentrationof the first doped region PAN in the shapes PH1, PH2, and could also beused in the example described in relation to FIGS. 2A to 2D to locallypass through the gap (DST) and join the first volume P in at least oneposition, and thus ensure electrical conduction between the anode ringPrg and the depleted anode region P.

Other combinations of the various examples and variants given above canbe considered and other shapes of patterns can be chosen to locallyincrease the dopant concentration in the first doped region PAN or elseto ensure electrical conduction between the anode ring Prg and thedepleted anode region P.

In summary, various exemplary embodiments of spad diodes SPD werepresented, with a high photon detection probability, operating atmoderate polarisation (for example less than 20V). The second dopedregion PAN allows the electric field to be concentrated, which inconventional cases leads to the formation of a pocket of charge carrierstrapped by a potential barrier, and causing parasitic triggers “lags”.

The various exemplary embodiments and variants of spad diodes SPDpropose opening an evacuation path in the potential barrier, by means ofa specific design of the doping of the semiconductor regions of theavalanche region of the diode, comprising in particular local variationsin the concentration of dopants of the second doped region PAN. Amonglocal variations in dopant concentration, areas of lower concentrationopen the evacuation paths in the potential barrier, and areas of greaterconcentration locally strengthen the electric field.

1. An integrated circuit, comprising: a semiconductor well doped with afirst type of dopant; and a single photon avalanche diode (SPAD) in thesemiconductor well, said SPAD including a PN junction between a firstregion doped with the first type of dopant and a second region dopedwith a second type of dopant opposite to the first type of dopant;wherein the first doped region has a shape that incorporates localvariations in dopant concentration that are configured to generate, inresponse to a voltage between the second doped region and thesemiconductor well that is greater than or equal to a level of abreakdown voltage of the PN junction, a monotonic variation inelectrostatic potential between the first doped region and thesemiconductor well.
 2. The integrated circuit according to claim 1,wherein the second doped region is located at a surface of thesemiconductor well at a position centered in a photosensitive area ofthe SPAD, wherein the first doped region comprises a first volume at aposition centered at a depth in contact with a bottom of the seconddoped region, and further including a second annular volume laterallysurrounding the first volume and at a depth remote from the second dopedregion but joining the depth of the first volume.
 3. The integratedcircuit according to claim 2, wherein the first volume and the secondannular volume are laterally spaced apart by a gap, and said localvariations in the concentration of dopants comprise areas of diffuseddopants in said gap having a lower concentration of dopants than in thefirst volume and the second annular volume.
 4. The integrated circuitaccording to claim 3, wherein the second annular volume furthercomprises a pattern locally passing through said gap to join the firstvolume in at least one position to provide electrical conduction betweenthe second annular volume and the first volume.
 5. The integratedcircuit according to claim 2, wherein the first volume and the secondannular volume are laterally joined together, and said local variationsin the concentration of dopants comprise areas in the first volumehaving a lower concentration of dopants than in the second annularvolume.
 6. The integrated circuit of claim 5, wherein the second annularvolume further comprises a pattern inside the first volume.
 7. A methodfor manufacturing an integrated circuit including a single photonavalanche diode (SPAD), comprising: implanting a first region doped witha first type of dopant in a semiconductor well doped with the first typeof dopant; implanting a second region doped with a second type of dopantopposite to the first type of dopant in the semiconductor well; whereinthe first and second regions form a PN junction of the SPAD; and whereinimplanting the first doped region comprises forming local variations indopant concentration that are configured to generate, in response to avoltage between the second doped region and the semiconductor well thatis greater than or equal to a level of a breakdown voltage of the PNjunction, a monotonic variation in the electrostatic potential betweenthe first doped region and the semiconductor well.
 8. The methodaccording to claim 7, wherein implanting the second doped regioncomprises implanting the second doped region at a surface of thesemiconductor well and at a position that is centered in aphotosensitive area of the SPAD, wherein implanting the first dopedregion comprises: a first implanting of a first volume at a positioncentered at a depth in contact with a bottom of the second doped region;and a second implanting of a second annular volume laterally surroundingthe first volume and at a depth remote from the second doped region butjoining the depth of the first volume.
 9. The method according to claim8, wherein the first volume and the second annular volume are laterallyspaced apart by a gap, and said local variations in the concentration ofdopants comprise areas of diffused dopants in said gap having a lowerconcentration of dopants than in the first volume and the second annularvolume.
 10. The method according to claim 9, wherein the secondimplanting of the second annular volume further comprises implanting apattern locally passing through said gap to join the first volume in atleast one position and provide electrical conduction between the secondannular volume and the first volume.
 11. The method according to claim8, wherein implanting the first volume and the second annular volumelaterally joins the first volume and second annular volume together,wherein the first implanting is made at a concentration of dopants lessthan the concentration of dopants of the second annular volume, and saidlocal variations in the concentration of dopants comprise areas in thefirst volume having a lower concentration of dopants than in the secondannular volume.
 12. The method according to claim 11, wherein the secondimplanting further comprises implanting a pattern inside the firstvolume.